OK. I watched your demo.
A lot of your issues will be smoothed out if you play a lot more 6v6. Things like game flow and strategy were working against you in this example. There were times you were in the wrong place and it cost you because your team couldn't assist.
Some tips:
Its ok to let your stickies lay. You shot a lot of stickies and blew them up on nothing. Then you reloaded constantly. This also announced your exact position. Also, sometimes you'd shoot at something and you blew them up before they even reached what you were fireing at. Once, you blocked the escape route for the enemy medic with stickies but you detonated them before he even got there. You would have had that kill but the soldier got it instead.
Lay more traps. Bread and butter demomanning. In 6v6 one of the best things you can do is shut down one of the choke points so your solies can take care of the other one.
Learn sticky placement. This is key for 1v1 deathmatching. You seemed to shoot behind your targets at close range with stickies. Then you'd realize you were missing and switch to your grenade launcher. But you wasted too much time with the missed stickies and you were mostly dead by the time the first pipe flew.
Stickies are your main weapon. Sometimes you'd throw a couple stickies, injure your target, and then swap to your nade launcher and wiff on 4 pipes and your target would escape or kill you. Just launch more stickies to finish 'em. Not every kill has to be finished with pipes.
Take care with your shots. You only get 2 or 3 and they have to hit or you're dead. If you shoot with purpose rather than spamming you'll be more successful.
Lower your sensitivity. Try playing with a lower sensitivity for a week. I think your aim will improve and you'll be more successful.
Be less suicidal. On the initial fight for the center point you killed yourself by jumping into 4 or 5 enemies almost everytime. Be a little more diliberate. Don't force it. Sometimes demo-bombs work, but the team has to be spread out first.
I hope this helps. Don't be too hard on yourself and keep practicing. If you ever want to duel or get in a server and work out anything just steam me.
Monkee.